The European Large Area ISO Survey VII: ROSAT observations of ELAIS sources

Abstract

We present a cross-correlation between the ELAIS 15$\mu$m ISO survey with the {\it ROSAT} (0.1-2 keV) all-sky survey and the pointed observations WGACAT source catalogue. The resulting sample contains 15 objects. Optical spectroscopic identifications exist for 13 objects: 6 broad-line QSOs, 4 narrow line galaxies or type-2 AGN (NLG) and 3 stars. We have used both the X-ray to IR luminosity flux ratio $f_x/f_{IR}$ and the X-ray hardness ratios diagnostics to estimate the amount of obscuration in these objects. The X-ray spectrum of the narrow-line galaxies does not present strong evidence for obscuration; however, the low $f_x/f_{IR}$ ratio combined with the high X-ray luminosities suggest that at least one of the narrow line galaxies is associated with an obscured Seyfert nucleus. 4 out of 6 QSOs present high $f_x/f_{IR}$ ratios and steep X-ray spectra with $\Gamma >2$. One QSO (ELAISC15-J133442+375736) at a redshift of z=1.89, has an abnormally low X-ray/IR flux ratio, with its infrared luminosity approaching that of an hyperluminous galaxy ($\sim 10^{12.98}{h}^{-2}{L}_{\odot }$). Finally, one radio-loud QSO is the hardest X-ray source in our sample, presenting strong evidence for a high absorbing column ($N_H\sim 10^{22}\mathrm{c}{\mathrm{m}}^{-2}$).

6 pages, 4 figures, in press MNRAS

References in corpus (4)

• XMM-Newton observations of the Lockman Hole V: time variability of the brightest AGN
• The Chandra Deep Field North Survey. VII. X-ray Emission from Lyman Break Galaxies
• The European Large Area ISO Survey V: a BeppoSAX hard X-ray survey of the S1 region
• The European Large Area ISO Survey VI - Discovery of a new hyperluminous infrared galaxy

Cited by in corpus (8)

• The European Large Area ISO Survey (ELAIS): The Final Band-merged Catalogue
• Candidate Type II Quasars from the Sloan Digital Sky Survey: II. From Radio to X-Rays
• A submillimetre difference between radio galaxies and radio quasars: evidence for quasar-heated dust and synchronized submillimetre and radio source activity
• The European Large Area ISO Survey IX: the 90 micron luminosity function from the Final Analysis sample
• FIRBACK IV: Towards the nature of the 170microns source population
• AKARI/IRC source catalogues and source counts for the IRAC Dark Field, ELAIS North and the AKARI Deep Field South
• The AKARI FU-HYU galaxy evolution program: First results from the GOODS-N field
• An Overdensity of Extremely Red Objects Around Faint Mid-IR galaxies